首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   304篇
  免费   23篇
林业   6篇
基础科学   2篇
  15篇
综合类   53篇
农作物   5篇
水产渔业   14篇
畜牧兽医   223篇
园艺   1篇
植物保护   8篇
  2021年   2篇
  2020年   7篇
  2019年   8篇
  2018年   11篇
  2017年   9篇
  2016年   8篇
  2015年   4篇
  2014年   9篇
  2013年   13篇
  2012年   9篇
  2011年   13篇
  2010年   15篇
  2009年   20篇
  2008年   15篇
  2007年   12篇
  2006年   5篇
  2005年   4篇
  2004年   7篇
  2003年   11篇
  2002年   3篇
  2001年   10篇
  2000年   7篇
  1999年   9篇
  1998年   14篇
  1997年   9篇
  1996年   12篇
  1995年   5篇
  1994年   2篇
  1993年   6篇
  1992年   9篇
  1991年   9篇
  1990年   8篇
  1989年   4篇
  1988年   3篇
  1987年   2篇
  1985年   2篇
  1984年   5篇
  1983年   4篇
  1982年   1篇
  1981年   1篇
  1980年   2篇
  1979年   1篇
  1977年   1篇
  1975年   2篇
  1974年   4篇
  1973年   5篇
  1972年   1篇
  1970年   1篇
  1958年   1篇
  1924年   1篇
排序方式: 共有327条查询结果,搜索用时 15 毫秒
111.
Apoptosis in the testis is required to ensure an efficient spermatogenesis. However, sometimes, defective germ cells that are marked for elimination during this process escape elimination in the testes, giving rise to ejaculates with increased percentages of abnormal and apoptotic spermatozoa and a high percentage of apoptotic bodies. Apoptosis markers in the ejaculate have been associated with low fertility, either in animals or humans. Therefore, the goal of this study was to investigate whether fresh equine semen contains apoptotic bodies [initially named Merocyanine 540 (M540) bodies] and to study the relationship between the quantity of these bodies and cell concentration, the volume of ejaculate, viability and motility. Moreover, we also studied whether the presence apoptotic bodies in fresh semen was related to the resistance of the stallion spermatozoa to being incubated at 37°C or being frozen and thawed. Fresh equine semen was stained with fluorescent dyes such as M540 and Annexin‐V. Active Caspase 3 was studied in fresh semen through Western blotting and immunofluorescence with a specific antibody. Sperm kinematics was assessed in fresh, incubated and thawed samples using computer‐assisted semen analysis, and viability was evaluated with the LIVE/DEAD Sperm Viability Kit. Overall, our results demonstrate for the first time the presence of apoptotic bodies in equine semen. The quantity of apoptotic bodies was highly variable among stallions and was positively correlated with Caspase 3 activity in fresh samples and negatively correlated with the viability and motility of stallion spermatozoa after the cryopreservation process.  相似文献   
112.
113.
114.
The clinical, pathological and biochemical findings of a study of 30 Poll Hereford, Hereford, Poll Hereford cross or Hereford cross calves affected with branched chain ketoacid dehydrogenase (BCKAD) complex deficiency or maple syrup urine disease (MSUD) are presented. In breeding studies, 6 of 21 calves from obligate heterozygote matings were affected with MSUD, suggesting the disease is inherited in an autosomal recessive manner. Calves were clinically affected from birth, but there were variations in the subsequent course of progressive deterioration of central nervous system function. Concentrations of the branched chain amino acids and keto acids were elevated in pre-suckle plasma and cerebellar water content was higher in affected calves. Activity of BCKAD complex was minimal in fibroblasts cultured from an affected calf. Spongiform encephalopathy and elevated ratios of the branched to straight chain amino acids in formalin fixed cerebral tissue were found in a stillborn foetus and a 3-month-old Hereford calf. These findings suggest the disease occurs prenatally and that a delayed form may exist.  相似文献   
115.
OBJECTIVE: To determine the diversity of Salmonella serotypes isolated from a large population of cull (market) dairy cows at slaughter. DESIGN: Cross-sectional study. SAMPLE POPULATION: Salmonella organisms isolated from the cecal-colon contents of 5,087 market dairy cows. PROCEDURE: During winter and summer 1996, cecal-colon contents of cull dairy cows at slaughter were obtained from 5 US slaughter establishments. Specimens were subjected to microbiologic culturing for Salmonella spp at 1 laboratory. Identified isolates were compared with Salmonella isolation lists published by the Centers for Disease Control and Prevention (CDC) and the National Veterinary Services Laboratory (NVSL) for approximately the same period. The Simpson diversity index was used to calculate the likelihood that Salmonella isolates selected randomly by establishment were different. RESULTS: Of 58 Salmonella serotypes identified, Salmonella ser. Montevideo was the most prevalent. Two of the top 10 CDC serotypes identified from in 1996, Salmonella ser. Typhimurium and S Montevideo, appeared on our top 10 list; 8 of the top 10 were found on NVSL listings. Thirty-one of 59 S. Typhimurium isolates were identified as DT104 and found at a west slaughter establishment, 30 during the winter and 1 during the summer. The greatest diversity of serotypes was at a southeast establishment during the summer; the least diversity was at a central establishment in the winter. CONCLUSIONS AND CLINICAL RELEVANCE: 58 Salmonella serotypes were isolated from market dairy cows at slaughter and could pose a threat for food-borne illness. Salmonella Montevideo was the most frequently isolated serotype and may contribute substantially to salmonellosis in dairy cattle.  相似文献   
116.
Four isolates of bovine adenovirus type 4 were recovered from Oregon cattle. One isolate was recovered from a 1-week-old calf with pneumoenteritis, and 1 isolate from an 8-month-old bull with fever and respiratory disease. Two isolates were recovered as latent viruses in testicular cell cultures. All 4 isolates of the virus were shown to have certain physical, chemical, biologic, and antigenic characteristics similar to previously described strains of bovine adenovirus type 4. Of 246 adult beef and dairy cattle in Oregon, 51% had serum-viral neutralizing antibodies to the type 4 virus at the 1:8 dilution level.  相似文献   
117.
118.
Enforcement of paragraph 11b of the German Animal Welfare Act is a responsibility of breeders and their organisations as well as executive local authorities. The Report on Defective Breeds of the Federal Ministry of Agriculture describes numerous breeding traits which are in conflict with animal welfare and gives valuable information for fancy or pet breeding. Yet a selection has to be made for taking legal actions, following specific criteria. With four examples different cases are presented, each requiring a different approach by the veterinarian authorities. Court decisions in Hessen concerning bans on breeding white cats and crested ducks show that the paragraph 11b is executable.  相似文献   
119.
This study was performed to evaluate plasma concentrations of anti‐Mullerian hormone (AMH) and the ovarian antral follicle population (AFP) in different genetic groups. Cyclic heifers (13 Bubalus bubalis [Murrah]; 15 Bos taurus [Holstein] and 10 Bos indicus [Gyr]) were maintained under the same management and were synchronized with two doses of 150 μg IM d‐cloprostenol administered 14 days apart. After the second d‐cloprostenol treatment, heifers had their ovaries scanned daily by ultrasound to define the day of ovulation. On the same day, the AFP was determined and a plasma sample was collected to measure AMH. Murrah heifers had less AFP (25.6 ± 2.1 follicles; p = 0.01) and plasma AMH concentration (0.18 ± 0.03 ng/ml; p < 0.001) than Gyr (60.0 ± 12.2 follicles and 0.60 ± 0.12 ng/ml of AMH); however, data were similar when compared to Holstein (35.9 ± 6.8 follicles and 0.24 ± 0.06 ng/ml of AMH) heifers. Regardless of genetic background, there was a positive relationship between the AFP and plasmatic AMH concentration (Murrah [r = 0.62; p < 0.01], Holstein [r = 0.66; p < 0.001] and Gyr [r = 0.88; p < 0.001]). Also, when heifers were classified according to high‐ or low‐AMH concentration based on the average within each genetic group, high‐AMH heifers had greater (p < 0.0001) AFP than low‐AMH heifers. In conclusion, both Murrah and Holstein heifers presented lower plasma AMH concentration and AFP when compared to Gyr.  相似文献   
120.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号